1. Field of the Invention
The present invention relates to an Asynchronous Transfer Mode (ATM) switching system and, in particular, to a control cell management method of an ATM switching system.
2. Background of the Related Art
An ATM communication divides a message into a plurality of ATM cells that each have 53 bytes. Once the cells are formatted, they are communicated through a transmission medium.
FIG. 1 is a block diagram illustrating a general ATM. The ATM switching system 10 includes an access switching apparatus 11, 14, an interconnection network apparatus 12, and an operation and maintenance apparatus 13. The access switching apparatus 11, 14 performs a switching function with the other base stations 1, 2, 3 to which it is connected, the interconnection network apparatus 12 interconnects each apparatus of the ATM switching system, and the operation and maintenance apparatus 13 manages and maintains the ATM switching system.
Generally, an ATM cell can be categorized as a user cell, for data transmission between users, and a control cell that processes and controls various calls in order to transmit the user cell. When base station 1 transmits a user cell, the user cell is transmitted to the access switching apparatus 11 of the ATM switching system 10, is routed in the interconnection network apparatus 12, and arrives in a particular destination after passing the access switching apparatus 14.
The control cell can be further categorized as a signaling cell, which transmits a control signal between ATM switching systems, and an Inter Processor Communication (IPC) cell that performs communication between each apparatus 11, 12, 13, 14 of the ATM switching system. The control cell is transmitted to a processor of the access switching apparatus 11 and performs a function, such as a call connection, a call release, a state report of the access switching apparatus 11, within the access switching apparatus.
A signaling cell can be further categorized as a signaling cell for call processing, a contact, a contact acceptance, and a setting. Signaling cells are used for a point-to-point contact set, a point-to-point release, a point-to-point release completion, an inquiry about a state of a pertinent apparatus, a restart, a restart acceptance in connection-management, an addition of another point, an addition acceptance of another point in association of one point-to-multipoint, a removal of the point, and a removal acceptance of the point.
An IPC cell can be used differently in each ATM switching system. An IPC cell is mainly used for communication between the operation and maintenance apparatus 13, managing the whole ATM switching system 10, and each apparatus of the ATM switching system 10. The IPC cell has information regarding the states, inspection, contact registration, and release of each apparatus of the ATM switching system 10.
The access switching apparatus 11, 14 of the ATM switching system 10 is constructed so as to include a plurality of the switching functions of the other base stations. Each access switching apparatus 11, 14 is functionally constructed to correspond with the base station with which it is connected.
FIG. 2 is a block diagram illustrating signaling cells for transmission and reception with base stations 1, 2 and IPC cells for transmission and reception with internal devices of the ATM switching system 10, when the access switching apparatus 11 is connected to two other base stations 1, 2.
FIG. 3 is a block diagram illustrating internal units of the access switching apparatus 11 of FIG. 1. The access switching apparatus 11 includes control (signaling) cell transmission and reception buffers 23a, 23b, 24a, 24b that transmit and receive signaling cells with base stations 1, 2, respectively. Access switching apparatus 11 has control cell (IPC) transmission and reception buffers 23c, 23d, 24c, 24d that transmit and receive IPC cells with the apparatuses of the ATM switching system 10. It has a signaling control cell First-In First-Out (FIFO) management unit 22 that manages the control (signaling) of the cell transmission and reception buffers 23a, 23b, 24a, 24b and the cell transmission and reception buffers 23c, 23d, 24c, 24d. Additionally, it has a processor 21 that controls the overall operation of the access switching apparatus 11.
In more detail, the first control (signaling) cell transmission FIFO 23a (hereinafter, a buffer is referred to as a FIFO) buffers a signaling cell to be transmitted to base station 1, the second control (signaling) cell transmission FIFO 23b buffers a signaling cell to be transmitted to base station 2, the first control (signaling) cell reception FIFO 24a buffers a signaling cell received from base station 1, and the second control (signaling) cell reception FIFO 24b buffers a signaling cell received from base station 2. Third and fourth control (IPC) cell transmission FIFOs 23c, 23d buffer IPC cells to be transmitted to particular internal devices of the ATM switching system 10, respectively. Third and fourth control (IPC) cell reception FIFOs 24c, 24d buffer IPC cells received from particular internal devices of the ATM switching system 10, respectively.
As depicted in FIG. 3, the access switching apparatus 11 accepts two access lines, buffers the signaling cells and the IPC cells in the eight control cell transmission and reception FIFOs 23a˜23d, 24a˜24d, and transmits the signaling cells and the IPC cells between the eight control cell transmission and reception FIFOs 23a˜23d, 24a˜24d and processor 21, by jointly controlling a data bus with the processor 21. Processor 21 can transmit or receive only one control cell at a time using the data bus. When communicating cells between the eight FIFOs 23a–23d, 24a–24d and the processor 21, the cells must be prioritized and the bus arbitrated to communicate the cells across the shared bus according to their respective priorities.
Processor 21 uses a Universal Test Operation Physical Layer Protocol Interface for ATM (UTOPIA) protocol as a master. The UTOPIA protocol is used between an ATM layer device and a physical layer device. The protocol has been standardized in an ATM forum and is capable of performing a seamless communication without affecting an ATM layer, which is a superior layer. The seamless communication is possible, regardless of the interface with a physical layer, due to a clarifying relationship between the ATM layer and a physical layer provided by the UTOPIA protocol.
When there is a control cell to be transmitted, the processor 21 transmits the control cell to the signaling control cell FIFO management unit 22, through an 8-bit data bus, using the UTOPIA interface.
Generally, the transmission of control cells precedes the reception of control cells in priority. Accordingly, when there are control cells to be received during the transmission of control cells, the cells to be received have to wait in the control cell reception FIFO 24a˜24d. 
After the transmission of the control cells is finished, the signaling control cell FIFO management unit 22 notifies the control cell reception FIFO, buffering the most recently arrived control cell, and requests a physical layer address of the pertinent control cell reception FIFO. Processor 21 selects the pertinent control cell reception FIFO to communicate the most recently arrived control cell.
As described above, when a control cell arrives during the transmission of other control cells, the related art ATM switching system does not recognize a first-arrived control cell but recognizes the most recently arrived control cell. When the transmission of control cells is finished, the reception processing of control cells starts with the most recently arrived control cell. Accordingly, the reception processing reverses the order of arrival for the control cells and may unduly delay their communication to the processor 21. In other words, processing of a first-arrived control cell in a pertinent control cell reception FIFO can not be performed until all other control cells that subsequently arrived in the other control cell reception FIFOs are processed.
Because the processing of control cells is not performed according to their order of arrival, the control signaling processing speed of the access switching apparatus and the performance of the ATM switching system are diminished.